This invention relates to a controlled capacitive filter for use in power circuits with active loads, and more particularly to an efficient controlled filter circuit in which the charge and discharge intervals of the filter capacitor are controlled by solid state switches.
In conventional power circuits with a filter capacitor connected directly across the output terminals of the full wave rectifier, and wherein an active device regulates the ripple voltage appearing on the filter capacitor to produce a constant dc output voltage (see FIG. 1), the filter capacitor is used inefficiently. As will be further explained, assuming that the capacitor voltage remains above the desired dc output voltage, the capacitor stores a relatively large amount of energy that is never used and also supplies energy when it is not necessary. By employing the improved single phase capacitive filter circuit herein described, the size of the filter capacitor needed for a given application is reduced due to more efficient control. In many applications, electrolytic type capacitors can be eliminated in view of the decreased value of capacitance needed. This is especially desirable in the case of long life applications and applications over extreme temperature ranges where electrolytic capacitors have reliability problems.